The invention describes a method and an apparatus for controlling the behavior of a generalized machine, in particular an internal combustion engine. It is the nature of the present invention to be applicable to a very wide class of regulatory processes, not confined merely to the control of the fuel-air mixture in an internal combustion engine. In particular, any operational variable of an engine or a vehicle, for example the ignition angle and the exhaust gas recycle rate, would be subject to control by the present invention.
The invention is based on a correction for the precise adaptation of one or more engine variables to prevailing engine conditions. For this purpose, sensors are provided that indicate prevailing states, for example the exhaust gas composition and on the basis of which the basic settings of other variables, for example the fuel-air mixture, are adjusted. The basic data and the corrective data are stored in suitable memories which, when interrogated, can provide an output signal that corrects the basic setting of the control variable. The corrective process is then guided by a closed-loop control which applies a continuous supervision of the behavior of the controlled variable in accordance with the prescribed values in the memory. In the closed-loop control process, the signal which is representative of the actual value of the controlled variable may be compared with a nominal value and the difference may be applied multiplicatively to the output of a controller that engages the corrective system.
In a particularly practical example of the invention, the variable which is monitored to generate the actual control value may be the exhaust gas composition as sensed by a so-called .lambda.-sensor but, in other cases, the sensor which generates the actual value of the control variable may be an engine detonation sensor, various extreme value and optimizing systems, a sensor for measuring the engine roughness, and the like. In general, the invention consists of sensing the magnitude of operational parameters, and to use this magnitude to address a memory which contains a characteristic data field. The memory generates an output variable which is applied to, for example, mechanical control elements that additionally correct the basic control variable, for example the fuel-air mixture. The output signal of the memory is then further influenced, for example multiplicatively, after comparison of the actual value of an engine variable with a set-point value to provide an overall, highly precise yet relatively simple and inexpensive control of the engine.
In a particular examplary but non-limiting example to be further described in detail below, the basic setting of the fuel mixture composition is provided by a carburetor which contains a corrective control element for providing adjustments to the fuel or air quantity which is being supplied. The monitored engine variable may be, for example, the exhaust gas composition as sensed by a .lambda.-sensor or some other suitable sensor.
In order to prevent dynamically incorrect adaptations, the integrated value of the control deviation is multiplied with the total value of the air factor .lambda. which is also stored in the above-mentioned memory and is finally applied to the final control element that sets the correction in the carburetor.
In the apparatus associated with the exemplary embodiment of the invention, using a carburetor for a basic control, a comparator which receives the .lambda.-sensor signal feeds an up-down counter whose output is fed to a multiplying circuit which multiplies this value with the total value of the air factor, i.e., the value .lambda..sub.0 +.DELTA..lambda.. The result is then applied via a digital-to-analog converter to the final control element. The use of a digital characteristic field to be used in association with the coarse basic control by a carburetor is known, for example, from the German Offenlegungsschrift No. 2 607 232. In that known system, the carburetor is so adjusted as to supply to the engine an amount of fuel which, in a first approximation, is proportional to the aspirated air current, thereby providing a basic but somewhat coarse adaptation. The precise adaptation of the carburetor is provided by the use of an electrically engaged control element which permits a regulation of the air pressure in an air chamber contained within the float chamber of the carburetor so as to change the flow of fuel through the main jet of the carburetor into the induction tube. The control process employs a read-only memory which, when addressed on the basis of one or more external operational variables of the engine, delivers an output signal which provides the corrected adaptation of the carburetor. The present invention is an improvement and further development of the known process of a digital control process and some of the basic elements of the known apparatus are contained in the illustration of FIG. 3 to be further described below.
In commonly used carburetors, the adaptation of the mixture composition for various operational domains of the engine cannot be made very precisely. Particular difficulties arise when the engine is being used in marginal domains and under extreme conditions, for example in an extreme lean-burn configuration where a relatively large variation of the air factor .lambda. becomes necessary. In the known system, the carburetor is equipped with at least one control element which is subjected to a superimposed control process based on a characteristic data field and which corrects the basic setting of the carburetor so as to follow the relatively complicated dependencies of the air factor. The control element is engaged preferably on the basis of two variables, for example for the throttle plate angle .alpha. and the engine speed n, or again the induction tube pressure p and the engine speed n, or even on the basis of the air flow rate Q in conjunction with the engine speed n. The magnitudes of these variables are detected by sensors and, after being suitably converted, are used for addressing a memory to retrieve the data stored therein. Basically, the memory will provide an output datum for any operational state of the engine. However, if the electronic corrective control fails, the basic setting of the carburetor is sufficiently accurate to permit at least a temporary operation of the engine.